Late Pleistocene-early Holocene paraglacial and fluvial sediment history in the Turbio valley, semiarid Chilean Andes

摘要

The transitional character of climatic conditions confers great relevance to paleoclimate studies in the semiarid region where glacial and Holocene geomorphologic records are scarce. Here we present the paraglacial and fluvial evolution of the Turbio valley (30°S) using both field observations and ~(14)C AMS chronology. Two key sites at the uppermost Turbio valley show glacial margins which likely formed during the 17-12ka Central Andean Pluvial Event and earlier 37-27ka episodes associated with glacial advances reported elsewhere in the semiarid Andes. Likewise, two episodes of subsequent paraglacial response are identified: a first episode corresponds to early Holocene fine-grained deposits (~11,500-7800calyr BP) extending far downstream (>40km) from the glacial margins. These deposits and coeval debris cones (~11,000-5500calyr BP) are the result of arid conditions with occasional runoffs that were unable to export sediments along the trunk valley. The second episode corresponds to disconformably overlying fluvial gravels extending ~70km downstream from the glacial margin, indicative of an increase in the fluvial transport capacity occurring not long after 5500calyr BP. Fluvial transport increase resulted from a late Holocene shift to wetter climate conditions, representing a forcing factor which enhanced the paraglacial response.